Recently an increased number of products referred to as magnetic beads and a number of products for efficient handling of these products have been presented. Magnetic bead technologies are used for diverse purposes such as isolating nucleic acids and proteins as well as viruses and whole cells. The adaptability and speed of this technique makes it ideal for high-throughput applications e.g. in 96 wells micro titre plates. The technique is also applicable for large scale applications, such as chromatography applications in liquid magnetically stabilised fluidised beds.
The magnetic beads are most commonly used in combination with attached ligands having affinity for different substances. The most commonly encountered examples are metal chelating ligands (of IMAC type) intended for use in combination with His-tags and glutathione intended for use in combination with GST (Gluthathione S transferase). Other examples are a variety of different IgG's with different specificity.
Preparation of beads encapsulating metallic materials and applications of magnetic beads has been described previously. Preparing magnetic beads where the bead is built up of different layers of material has also been presented earlier.
U.S. Pat. No. 5,834,121 describes composite magnetic beads. Polymer coated metal oxide particles that are encapsulated in a rigid and solvent stable polymer of vinyl monomers in order to retain the metal oxide particles during harsh conditions. The primary beads are enclosed in a micro porous polymer bead which is capable of swelling in organic solvents and allowing for further functionalisation in order to be useful for organic synthesis. This procedure is aiming for hydrophobic beads.
U.S. Pat. No. 6,204,033 describes preparation of polyvinyl alcohol-based magnetic beads for binding biomolecules. Preparation of magnetic beads by polyvinyl alcohol in water containing magnetic particles. The final beads contain hydroxyl functionalities that can be further derivatized in order to couple biomolecules. It is claimed that these magnetic beads can be grafted with vinyl monomers carrying various functional groups.
U.S. Pat. No. 6,274,387 describes a magnetic carrier, preparation thereof, and a method of extraction of nucleic acid. Particulate silica containing magnetic material is covered with polyacryl amide.
EP 0179039 describes polymer coated metal surfaces. Dextran carrying imino diacetate groups are allowed to attach to a metal surface. Several rounds of activation and coupling of dextran is required to build up a particle. To the dextran various ligands can be attached.
In J. of Polymer Science: Part A: Polymer Chemistry p. 1342-1356, (2005), preparation and clinical application of immunomagnetic latex is described by Wang et al. Magnetic metal oxide particles were encapsulated in poly(methyl methacrylate) [PMMA]. In order to add —COOH functional groups to the surface, a core of poly(methyl methacrylate-co-methacrylic acid) [P(MMA-MAA)] was added.
In spite of the relatively large number of magnetic beads described today, there is still a need of porous beads adapted to large as well as lab scale applications. Especially, there is a need of biocompatible magnetic beads intended for cell separation/cultivation which are free of metal leakage that might have a negative effect on the cells.